4 files changed, 249 insertions, 7 deletions

diff --git a/crates/ra_syntax/src/algo.rs b/crates/ra_syntax/src/algo.rs
index 46680a08f..f33d2ad4e 100644
--- a/crates/ra_syntax/src/algo.rs
+++ b/crates/ra_syntax/src/algo.rs
@@ -3,6 +3,7 @@ pub mod visit;
 use std::ops::RangeInclusive;
 
 use itertools::Itertools;
+use ra_text_edit::TextEditBuilder;
 use rustc_hash::FxHashMap;
 
 use crate::{
@@ -63,6 +64,18 @@ pub enum InsertPosition<T> {
     After(T),
 }
 
+pub struct TreeDiff {
+    replacements: FxHashMap<SyntaxElement, SyntaxElement>,
+}
+
+impl TreeDiff {
+    pub fn into_text_edit(&self, builder: &mut TextEditBuilder) {
+        for (from, to) in self.replacements.iter() {
+            builder.replace(from.text_range(), to.to_string())
+        }
+    }
+}
+
 /// Finds minimal the diff, which, applied to `from`, will result in `to`.
 ///
 /// Specifically, returns a map whose keys are descendants of `from` and values
@@ -70,12 +83,12 @@ pub enum InsertPosition<T> {
 ///
 /// A trivial solution is a singletom map `{ from: to }`, but this function
 /// tries to find a more fine-grained diff.
-pub fn diff(from: &SyntaxNode, to: &SyntaxNode) -> FxHashMap<SyntaxElement, SyntaxElement> {
+pub fn diff(from: &SyntaxNode, to: &SyntaxNode) -> TreeDiff {
     let mut buf = FxHashMap::default();
     // FIXME: this is both horrible inefficient and gives larger than
     // necessary diff. I bet there's a cool algorithm to diff trees properly.
     go(&mut buf, from.clone().into(), to.clone().into());
-    return buf;
+    return TreeDiff { replacements: buf };
 
     fn go(
         buf: &mut FxHashMap<SyntaxElement, SyntaxElement>,
diff --git a/crates/ra_syntax/src/ast.rs b/crates/ra_syntax/src/ast.rs
index fdffd8cb1..1b2ce921a 100644
--- a/crates/ra_syntax/src/ast.rs
+++ b/crates/ra_syntax/src/ast.rs
@@ -5,7 +5,7 @@ mod traits;
 mod tokens;
 mod extensions;
 mod expr_extensions;
-mod edit;
+pub mod edit;
 pub mod make;
 
 use std::marker::PhantomData;
diff --git a/crates/ra_syntax/src/ast/edit.rs b/crates/ra_syntax/src/ast/edit.rs
index c65899812..03f3b5fbb 100644
--- a/crates/ra_syntax/src/ast/edit.rs
+++ b/crates/ra_syntax/src/ast/edit.rs
@@ -1,14 +1,21 @@
 //! This module contains functions for editing syntax trees. As the trees are
 //! immutable, all function here return a fresh copy of the tree, instead of
 //! doing an in-place modification.
+use std::{iter, ops::RangeInclusive};
 
 use arrayvec::ArrayVec;
-use std::ops::RangeInclusive;
+use rustc_hash::FxHashMap;
 
 use crate::{
     algo,
-    ast::{self, make, AstNode},
-    InsertPosition, SyntaxElement,
+    ast::{
+        self,
+        make::{self, tokens},
+        AstNode, TypeBoundsOwner,
+    },
+    AstToken, Direction, InsertPosition, SmolStr, SyntaxElement,
+    SyntaxKind::{ATTR, COMMENT, WHITESPACE},
+    SyntaxNode, T,
 };
 
 impl ast::FnDef {
@@ -31,6 +38,218 @@ impl ast::FnDef {
     }
 }
 
+impl ast::ItemList {
+    #[must_use]
+    pub fn append_items(&self, items: impl Iterator<Item = ast::ImplItem>) -> ast::ItemList {
+        let mut res = self.clone();
+        if !self.syntax().text().contains_char('\n') {
+            res = res.make_multiline();
+        }
+        items.for_each(|it| res = res.append_item(it));
+        res
+    }
+
+    #[must_use]
+    pub fn append_item(&self, item: ast::ImplItem) -> ast::ItemList {
+        let (indent, position) = match self.impl_items().last() {
+            Some(it) => (
+                leading_indent(it.syntax()).unwrap_or_default().to_string(),
+                InsertPosition::After(it.syntax().clone().into()),
+            ),
+            None => match self.l_curly() {
+                Some(it) => (
+                    "    ".to_string() + &leading_indent(self.syntax()).unwrap_or_default(),
+                    InsertPosition::After(it),
+                ),
+                None => return self.clone(),
+            },
+        };
+        let ws = tokens::WsBuilder::new(&format!("\n{}", indent));
+        let to_insert: ArrayVec<[SyntaxElement; 2]> =
+            [ws.ws().into(), item.syntax().clone().into()].into();
+        insert_children(self, position, to_insert.into_iter())
+    }
+
+    fn l_curly(&self) -> Option<SyntaxElement> {
+        self.syntax().children_with_tokens().find(|it| it.kind() == T!['{'])
+    }
+
+    fn make_multiline(&self) -> ast::ItemList {
+        let l_curly = match self.syntax().children_with_tokens().find(|it| it.kind() == T!['{']) {
+            Some(it) => it,
+            None => return self.clone(),
+        };
+        let sibling = match l_curly.next_sibling_or_token() {
+            Some(it) => it,
+            None => return self.clone(),
+        };
+        let existing_ws = match sibling.as_token() {
+            None => None,
+            Some(tok) if tok.kind() != WHITESPACE => None,
+            Some(ws) => {
+                if ws.text().contains('\n') {
+                    return self.clone();
+                }
+                Some(ws.clone())
+            }
+        };
+
+        let indent = leading_indent(self.syntax()).unwrap_or("".into());
+        let ws = tokens::WsBuilder::new(&format!("\n{}", indent));
+        let to_insert = iter::once(ws.ws().into());
+        match existing_ws {
+            None => insert_children(self, InsertPosition::After(l_curly), to_insert),
+            Some(ws) => {
+                replace_children(self, RangeInclusive::new(ws.clone().into(), ws.into()), to_insert)
+            }
+        }
+    }
+}
+
+impl ast::RecordFieldList {
+    #[must_use]
+    pub fn append_field(&self, field: &ast::RecordField) -> ast::RecordFieldList {
+        self.insert_field(InsertPosition::Last, field)
+    }
+
+    #[must_use]
+    pub fn insert_field(
+        &self,
+        position: InsertPosition<&'_ ast::RecordField>,
+        field: &ast::RecordField,
+    ) -> ast::RecordFieldList {
+        let is_multiline = self.syntax().text().contains_char('\n');
+        let ws;
+        let space = if is_multiline {
+            ws = tokens::WsBuilder::new(&format!(
+                "\n{}    ",
+                leading_indent(self.syntax()).unwrap_or("".into())
+            ));
+            ws.ws()
+        } else {
+            tokens::single_space()
+        };
+
+        let mut to_insert: ArrayVec<[SyntaxElement; 4]> = ArrayVec::new();
+        to_insert.push(space.into());
+        to_insert.push(field.syntax().clone().into());
+        to_insert.push(tokens::comma().into());
+
+        macro_rules! after_l_curly {
+            () => {{
+                let anchor = match self.l_curly() {
+                    Some(it) => it,
+                    None => return self.clone(),
+                };
+                InsertPosition::After(anchor)
+            }};
+        }
+
+        macro_rules! after_field {
+            ($anchor:expr) => {
+                if let Some(comma) = $anchor
+                    .syntax()
+                    .siblings_with_tokens(Direction::Next)
+                    .find(|it| it.kind() == T![,])
+                {
+                    InsertPosition::After(comma)
+                } else {
+                    to_insert.insert(0, tokens::comma().into());
+                    InsertPosition::After($anchor.syntax().clone().into())
+                }
+            };
+        };
+
+        let position = match position {
+            InsertPosition::First => after_l_curly!(),
+            InsertPosition::Last => {
+                if !is_multiline {
+                    // don't insert comma before curly
+                    to_insert.pop();
+                }
+                match self.fields().last() {
+                    Some(it) => after_field!(it),
+                    None => after_l_curly!(),
+                }
+            }
+            InsertPosition::Before(anchor) => {
+                InsertPosition::Before(anchor.syntax().clone().into())
+            }
+            InsertPosition::After(anchor) => after_field!(anchor),
+        };
+
+        insert_children(self, position, to_insert.iter().cloned())
+    }
+
+    fn l_curly(&self) -> Option<SyntaxElement> {
+        self.syntax().children_with_tokens().find(|it| it.kind() == T!['{'])
+    }
+}
+
+impl ast::TypeParam {
+    #[must_use]
+    pub fn remove_bounds(&self) -> ast::TypeParam {
+        let colon = match self.colon_token() {
+            Some(it) => it,
+            None => return self.clone(),
+        };
+        let end = match self.type_bound_list() {
+            Some(it) => it.syntax().clone().into(),
+            None => colon.clone().into(),
+        };
+        replace_children(self, RangeInclusive::new(colon.into(), end), iter::empty())
+    }
+}
+
+#[must_use]
+pub fn strip_attrs_and_docs<N: ast::AttrsOwner>(node: &N) -> N {
+    N::cast(strip_attrs_and_docs_inner(node.syntax().clone())).unwrap()
+}
+
+fn strip_attrs_and_docs_inner(mut node: SyntaxNode) -> SyntaxNode {
+    while let Some(start) =
+        node.children_with_tokens().find(|it| it.kind() == ATTR || it.kind() == COMMENT)
+    {
+        let end = match &start.next_sibling_or_token() {
+            Some(el) if el.kind() == WHITESPACE => el.clone(),
+            Some(_) | None => start.clone(),
+        };
+        node = algo::replace_children(&node, RangeInclusive::new(start, end), &mut iter::empty());
+    }
+    node
+}
+
+#[must_use]
+pub fn replace_descendants<N: AstNode, D: AstNode>(
+    parent: &N,
+    replacement_map: impl Iterator<Item = (D, D)>,
+) -> N {
+    let map = replacement_map
+        .map(|(from, to)| (from.syntax().clone().into(), to.syntax().clone().into()))
+        .collect::<FxHashMap<_, _>>();
+    let new_syntax = algo::replace_descendants(parent.syntax(), &map);
+    N::cast(new_syntax).unwrap()
+}
+
+// Note this is copy-pasted from fmt. It seems like fmt should be a separate
+// crate, but basic tree building should be this crate. However, tree building
+// might want to call into fmt...
+fn leading_indent(node: &SyntaxNode) -> Option<SmolStr> {
+    let prev_tokens = std::iter::successors(node.first_token(), |token| token.prev_token());
+    for token in prev_tokens {
+        if let Some(ws) = ast::Whitespace::cast(token.clone()) {
+            let ws_text = ws.text();
+            if let Some(pos) = ws_text.rfind('\n') {
+                return Some(ws_text[pos + 1..].into());
+            }
+        }
+        if token.text().contains('\n') {
+            break;
+        }
+    }
+    None
+}
+
 #[must_use]
 fn insert_children<N: AstNode>(
     parent: &N,
diff --git a/crates/ra_syntax/src/ast/extensions.rs b/crates/ra_syntax/src/ast/extensions.rs
index 0433edb84..8c5ece65d 100644
--- a/crates/ra_syntax/src/ast/extensions.rs
+++ b/crates/ra_syntax/src/ast/extensions.rs
@@ -4,7 +4,7 @@
 use itertools::Itertools;
 
 use crate::{
-    ast::{self, child_opt, children, AstNode, SyntaxNode},
+    ast::{self, child_opt, children, AstChildren, AstNode, SyntaxNode},
     SmolStr, SyntaxElement,
     SyntaxKind::*,
     SyntaxToken, T,
@@ -203,6 +203,16 @@ impl ast::ImplBlock {
     }
 }
 
+impl ast::AttrsOwner for ast::ImplItem {
+    fn attrs(&self) -> AstChildren<ast::Attr> {
+        match self {
+            ast::ImplItem::FnDef(it) => it.attrs(),
+            ast::ImplItem::TypeAliasDef(it) => it.attrs(),
+            ast::ImplItem::ConstDef(it) => it.attrs(),
+        }
+    }
+}
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum StructKind {
     Tuple(ast::TupleFieldDefList),